The present invention relates to a photoreceptor, and more particularly to a novel photoreceptor having a photosensitive layer comprising a specific azo compound.
Those which have hitherto been widely used as the photoreceptor in the electrophotographic process are inorganic photoreceptors having a photosensitive layer comprised principally of an inorganic photoconductive compound such as selenium, zinc oxide, cadmium sulfide, silicon, or the like. These, however, are not necessarily satisfactory in the sensitivity, thermal stability, moisture resistance, durability, and the like. For example, selenium is difficult of manufacture because, when crystallized, its characteristics as a photoreceptor becomes deteriorated. And it tends to be crystallized due to heat or finger marks, whereby its property as the photoreceptor becomes deteriorated. Cadmium sulfide also is problematic in the moisture resistance as well as in the durability. And so is zinc oxide in the durability.
For the purpose of overcoming such disadvantages of these inorganic photoreceptors, the research and development of organic photoreceptors having photoesensitive layer comprised principally of any of various organic photoconductive compounds having become extensively carried on in recent years. For example, Japanese Patent Examined Publication No. 10496/1975 describes an organic photoreceptor having a photosensitive layer containing both poly-N-vinylcarbazole and 2,4,7-trinitro-9-fluorenone. This photoreceptor, however, is not necessarily satisfactory in the sensitivity as well as in the durability. In order to get rid of such shortcomings, attempts have been made to allot the carrier-generating function and carrier-transport function to different materials to thereby develop a higher performance-having organic photoreceptor. Such a function-separated-type photoreceptor permits a wide selection of appropriate materials for the respective functions thereof, and by using them any discretional characteristic-having photoreceptors can be relatively easily produced. Thus, many researches have been carried on for the development of photoreceptors of this type.
In the above-mentioned function-separated-type photoreceptors, as the carrier-generating substance thereof a variety of compounds have been proposed. An example of those inorganic compounds usable as the carrier-generating substance is the amorphous selenium described in, e.g., Japanese Patent Examined Publication No. 16198/1968. This is to be used in combination with an organic photoconductive compound, but the carrier-generating layer comprised of the amorphous selenium is still not improved to get rid of the disadvantage that the layer is crystallized by heat to cause its characteristic to be deteriorated.
Also, there have been many proposals for electrophotographic photoreceptors which use organic dyes or pigments as the carrier-generating substance. For example, those electrophotographic photoreceptors which contain bisazo compounds in the photosensitive layer thereof are already of the prior art found in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as Japanese Patent O.P.I. Publication) Nos. 22834/1979, 73057/1980, 117151/1980 and 46237/1981. These bisazo compounds, however, are not necessarily satisfactory in the sensitivity, residual potential or stability against the repetitional use, and limits the selectable range of carrier-transport substances, and thus are unable to adequately satisfy diverse requirements in the electrophotographic process.
Further, in recent years, as the light source for the photoreceptor, gas lasers such as Ar laser, He-Ne laser, etc., and semiconductor lasers have begun to be used. These lasers are characterized by permitting their time-series ON/OFF operation, and are promising as the light source for those image-processing function-having copiers including intelligent copiers or for those output printers used for computers. Among other things, semiconductor lasers attract attention for the reason that their nature requires no electric signal/light signal conversion elements such as acoustic elements, and they enable making their devices to be of a smaller size and a lighter weight. However, not only is the semiconductor laser's output lower than that of the gas laser but also its oscillating wavelength is on the longer wavelength side (not less than about 780 nm), and in contrast, the spectral sensitivity of conventional photoreceptors is on the far shorter wavelength side than that of the semiconductor laser. Accordingly, conventional photoreceptors can not be used as the photoreceptor for which the semiconductor laser is used as the light source.